Of SANS and IOS

Anyone knows What The FARKS is that IOs unit the HP SAN folk keep
talking about? Like in, yeah, this thing can take 2000 IOS per second.
How many bytes is an IOs supposed to be? An IO==Device blocksize or WTF?
It seems like most that have bought a SAN knows how many IOs it is
worth, but noone knows what an IOs is (yeah, Input Output Operation)....
I know how many Gbps i need, not how many IOs, how do i go from one to
the other?
My guess is that its the blocksize of the fs that i plan to use. If so,
ican divide my X Gbps between 8 to get GBps, then between 4000 to get
the blocks per seconds i need....would that map into IOS?
Treacherous salesmen everywhere!
Lex